1. Field of the Invention
The present invention relates generally to building construction and more specifically to lateral load-resisting truss segments of buildings, including segments of walls, floors, roofs, ceilings, and the like.
2. Description of the Related Art
It is a well-known principle of building construction that the building must include higher-strength structural segments that resist and transfer loads. These load-transfer segments can be provided in the walls, floors, roof, ceilings, and other portions of the building. For example, the building walls typically include segments that transfer lateral (shear) loads down into the building foundation. Shear loads often result from winds, earthquakes, and the like. In conventional building construction, the shear loads are transmitted horizontally through framing generally known in the industry as diaphragms, and down the lateral load-resisting wall segments to an element that is connected to the foundation. Since loads are naturally transmitted through the stiffest element, the lateral load-resisting wall segments can be positioned at different locations within the overall length of the wall of the building, so long as these wall segments are sufficient in quantity and strength to transmit the expected shear loads. One type of lateral load-resisting wall segment is a shear wall. A shear wall acts as a unitary load-transferring segment. An exemplary shear wall design is disclosed in the '767 patent. This shear wall includes holdowns for securing the shear walls to structural elements below, such as the building foundation.
In order to illustrate these concepts, consider FIG. 1, which shows a conventional building construction. In particular, FIG. 1 shows a two-story house 10 built on a foundation 12. The house 10 includes a lower wall 14 and an upper wall 16. A diaphragm or framing system includes horizontal plates 18 that frame the independent wall segments of walls 14 and 16. Each wall includes a plurality of wall segments 20 and 22. The wall segments 20 are shear walls (each denoted by a large X), which transfer horizontal loads to the foundation below. The wall segments 22 are so-called “non-shear” walls, because they are not designed to transfer lateral loads. The wall segments 22 typically comprise standard or simple frames, and may include a number of vertical studs therein. As shown, the wall segments 22 can include wall openings, such as the windows 24 and the doors 26.
With continued reference to FIG. 1, when the walls 14 and 16 experience shear forces F (which may or may not be equal to one another), these loads are transferred horizontally through the horizontal plates 18 and then downward through the shear walls 20 to the foundation 12.
A typical shear wall comprises wooden members joined together to form a frame structure, with a planar plywood sheathing attached on one or both sides for stability and rigidity. Ordinarily, the plywood is nailed into the frame members. This configuration is expensive because it requires a great deal of plywood and the installation process is labor-intensive. Another disadvantage of this configuration is that the nails often fail and inaccurate nailing is the cause of many lawsuits against building contractors. The nails often miss the studs or are nailed too far into the plywood, thus causing the wall segment to lose some of the lateral load-resisting capacity of the plywood. This can result in excessive wall movement, manifested by cracks and possibly building failure.
While described in the context of walls and wall segments, many of these same problems exist for floor, roof, ceilings, and other building portions. That is, floors, roofs, ceilings, and the like also typically involve plywood nailed into diaphragms, which causes the aforementioned problems: labor-intensive installation and elevated risk of movement and failure.